Minimization of Tin Whisker Growth for Ultra-Low Tin Whisker Applications

Establishment of common metrics for testing of lead free electrodeposits used in electronics applications in the form of industry standard JEDEC JESD201 has resulted in common ground for analysis and reporting of tin whisker growth. Successful satisfaction of JESD201's maximum whisker length (MWL) requirements, currently set at MWL = 40 microns for Class II components for both the high temperature/humidity and ambient test conditions and MWL = 45 microns for the thermal cycling requirement, is now common. However, some high-reliability end users expect component suppliers to meet MWL requirements beyond that of the JEDEC standard, and it is conceivable that further reduction of JEDEC MWL requirements may ultimately be required; MWL requirements of 30 microns, 20 microns or even less is possible in the future. This paper will discuss several methods for satisfying future ultra-low tin whisker growth requirements. The first method is the development of a new matte tin electroplating chemistry that produces a deposit which exhibits preferred grain morphology. The second method is the development of a new tin-silver alloy electroplating process which deposits similar to 95% tin / 5% silver alloy. Tin whisker results from these deposits obtained from both laboratory and production environments will be provided, as well as discussions on mechanistic explanations for the reduced tin whisker growth observed using these two methods.